Assuming your ground connection is soldered properly, the culprit is likely to be the switch which is responsible for turning that lamp on and off. Find the relay, find the switch, clean and adjust as necessary.

I assume you mean "cupped" inserts when you say warped.
I used Varathane on my woodrail instead of crazy glue, I think it to be clearer when dry.

Assuming you replaced bulb too but it was not mentioned. Sounds like your problem is elsewhere than the socket, usually lamps turn on via a relay or stepper contact. You might have a dirty contact/switch for the lamp that is flickering.

https://pinside.com/pinball/forum/topic/vids-guide-to-ultimate-playfield-restoration/page/17#post-1717646

I assumed a properly functioning bulb, too.

I am more or less using Vid's guide for fixing my non-flat playfield inserts. He has some great instructions there and deserves most of the credit. Here is a high level overview of the steps I am going through. If you need any assistance with a particular step let me know.:

1. Remove original inserts from playfield
2. Scan the inserts at 300 ppi
3. Use the scanned image and photoshop to create an 8.5 x 11 page at the same 300 ppi for easy print size matching (ie when the image is printed its the exact size you need). Using photoshop touch up all the inserts and print the new graphics onto waterslide decal paper.
4. Sand the inserts flat, taking off the original silkscreen graphic OR buy some brand new inserts from pbresource I plan on taking the former approach and using the originals.
5. Once flat, put a thin layer of clear over the now blank insert, sand flat, polish out
6. Apply your new insert decals atop the layer of clear
7. Put inserts back into the playfield
8. Using Vid's method, put a final layer of clear over the insert, sealing the decal in, as well as sealing between the insert and the wood playfield. Mask around the insert and sand flat/polish

It should be noted that I am currently working on step 3 of this process so I can't comment on how steps 4 through 8 will turn out. Luckily I am working on a playfield that I don't so much care about getting perfect so its good for practice.

I'm not sure if this is THE approach to fixing this problem, but its one that I think should end up working pretty well.

On the flickering bulb issue. (assuming you have already replaced the socket and bulb) If you have cleaned and adjusted the relay and the bulb still flickers then you may want to check the jones plug. If the jones plug is dirty then take wire brush or 600 grit sand paper and clean them. After doing this you will want to use 90% iso rubbing alcohol to do the final cleaning. I also find that rubbing alcohol on the female plug cleans out all the debris. Many strange problems seem to disappear after a good jones plug cleaning.

if the lamp is lit via a switch check contacts on that switch
sounds like the a dirty switch if you replace the socket

2 part automotive clear. If you need suggestions let me know. I already bugged Vid enough and can provide the answers he gave me

Your light socket could be dim even with a new socket and wiring soldered correctly as the 5 upper lights are controlled through separate Score Motor Switches for each lamp. You most likely have a contact that needs cleaning/gaping. Find the Score Motor Switch for that light on your Schematic and you should be set.

Ken

lol

Some good info here as well. Not tried it but did buy the stuff that was recommended.

http://www.passionforpinball.com/jjresto2.htm

I have a stock of 1" NOS inserts if you need any.